Ham Radio News!
Ham Radio Videos!
HF & Shortwave
RFI Tips and
Support The Site
Vhf and Up
2 Meter Bobtail Rover
(How to Upset the Neighbors)
Tom builds something in this
project just to upset the neighbors!
"What is that "Thing" on
top of his Jeep!" Said the neighbors.
"A tent frame, a
portable clothes line, some new fangled TV antenna?
Sorry neighbors! None of the above.
Beam project all ready to go roving and irritate more
neighbors, fellow employees, and wild
the cops will turn their heads too, but to a true ham, isn't it a
That "thing" on top of Tom's Jeep is his new
homebrew 2 meter Bobtail Beam designed for roving around the countryside.
Let's find out how Tom built it. Get in, fasten your
seat belts and hang
Bobtail Beam Posing for
camera with wings spread and feet on the ground
using "Quad Pod" base
fixture designed by Tom
Elements "Magically Enhanced" by
Windows Technology to Show Detail
Camera position is direction of
Even if you purchase
absolutely everything new it should cost under $50 to make and less if you
are a great scrounger....
2 Meter version
8' 14ga speaker wire $5.71
6 1/4-20 x 1.5 Brass
2 1/2" PVC Tee $0.64
4 1/2" PVC Elbow $0.96
1/2" PVC Cross $1.02
1 1/2" PVC Cap $0.28
2 1/2" x 10' PVC
6 1/4" x 14ga ring lugs $0.96
6 #4 x 14ga ring lugs
1 1/8" x 12" K&S Brass Tubing $0.79
1 5/32 x 12" K&S Brass Tubing $0.89
1 Pound 3/32 x 36" Brazing Rod
2 7/64 twist Drill Bits $3.85
6 1/4-20 nylon wing nuts
1 SO-239 Chassis Connector $1.50
1 15' RG-8 w PL259 coax
2 6/32 x 1-3/4 bolt $0.30
2 6/32 nut $0.10
masons cord $1.00
4 6"x6"x 3/4" Plywood Scrap $0.00
Steel Wing Nut $0.25
2 1/4" steel flat washer $0.10
12" nylon cable ties $1.00
about 22 feet including mast.
(Your total length may be
depending on your construction, errors,
NOTE: XXX = See
(These formulas are
not exact but should be close.)
Front Elements 248/freqmhz = length in feet
by 12 = inches)
Reflector Elements 263 / freqmhz = length
in feet )
multiply by 12 = inches)
Spacing = .15 X one wavelength
1 Wavelength = 11808 / freq =
GETTING STARTED - The 2 Meter Version
(Please note that some of the pictures in this
project could be showing the
70cm band antenna that Tom is also
working on and is not an error.
They are used this way only to show
physical constructions details which are much
the same for both
Caution with hand tools!
Eye protection is a good
Don't poke an eye with the
Be careful cutting PVC
2 @ 5" (Center Spreaders)
2 @ 11" (End
4 @ 40" (Side Spreaders)
1 @ 20" (Vertical
1 @ 48" (Mast)
Drill a 7/64" hole in the ends of the
Before starting, fashion a bolt holder from
6"x6"scrap of 3/4" plywood (or similar material)
as you are not
going to be able to hold the bolts in
your fingers without burning or
Drill a 1/4" hole in the middle of
the plywood scrap
and secure the brass bolt with washers and a nut.
Make sure it is tight... Drill the 7/64 hole
deep with a drill press
or electric hand drill. A new (sharp) twist
is recommended as is having an extra
bit and a spare bolt
around. This be handy if you
break a bit as I did. Only five bolts are
Cut five lengths of 3/32 brazing rod to
23". To cut
the brazing rod you can make a deep score with the
of a metal file and snap the rod. Insert the rods
into the bolts and
solder using a small torch or heavy
duty iron. Don't worry about the
exact length at this
time as they will be trimmed later.
(or file) a 9/16" hole in one of the PVC Tee's
for mounting the SO-239
Connector. Once the
connector is in place, drill holes to clear, then
Drill a 3/32 hole for the driven element in the
opposite the 9/16" hole.
In this photo you will notice the
SO-239 is mounted to the bottom of the front
element. The driven element is attached (inside PVC T)
directly to the
end tip of the SO-239 and extends up through the front element.
feed line is routed as per instructions below using the coax choke
the center "boom" and down to the rig. (Photo above not to
scale for 2 meters)
Drill 1/4" holes in
the rest of PVC Tee's and elbows
for mounting bolts. (see photo)
Photo showing ends with
elements, ring lugs and wire extending from
Prepare two 14 ga wires with 1/4" ring lugs so that
centers between lugs are 40 3/16". These are the
common "ground" wire
for the three rear elements.
Prepare two 14 ga wires with a 1/4:
ring lug on one
end and a #4 ring lug on the other end. Center
center each cable is about 39 11/16". When
the two cables are
connected to the SO-239 connector,
the end rings will be 40 3/16"center
Lay the PVC frame pieces out on the ground
assemble. The front row to back row spacing is 12"
to element. The horizontal spacing
is 40 3/16" element to element. Be
sure the center
cross is vertical - glue all joints, or if you wish
make the antenna "portable" you may want to
use sheet metal
screws or nuts and bolts to assemble
XXX To prepare the driven element, nest a 1" length
5/32 K&S tubing with 1" of 1/8" K&S tubing and insert
23" piece of 3/32 rod into the center of the
XXX 1/8" tube. The 5/32" tube should fit neatly
the center conductor of the PL-239 connector. Use a
or heavy duty iron and solder.
To prepare the driven element, file
3/8" of one end of
a 23" long 3/32" rod to fit into the center
(tip end, not connector end) of a SO-239 socket.
end of the rod, then solder it into the tip part
For the reflectors, trim three of the rod/bolt
21 9/16" The length is measured from
the tip to the point where the
bolt touches the
Photo of rear "center" element on
reflector portion of antenna.
Notice connections to each outside
element using speaker wire.
For the two
front directors, trim the elements to
20 1/4"> (cut longer for
For the time being, leave the driven element long,
assemble the "grounds" and elements to the frame.
the RG-8 coax to the SO-239 connector. Make a
coax choke by wrapping
five turns around the center
spreader closest to the connector. Secure
cable ties and dress the rest of the coax to the mast.
Elevate the antenna about 4' to 6' in
the air and at
least a wavelength away horizontally from any
objects. Apply low power at the desired operating
and trim the driven element for the best SWR.
The length should be
about the same as the reflectors.
If you cut too short, the driven
element may be lengthened
with a piece of the 1/8" K&S tubing - be
sure to solder
After trimming the driven element, trim
two directors to the same length to optimize the
My own personal preference is to paint everything
flat grey spray paint. This will prevent rust
and the inevitable UV
damage to the PVC piping
if you are going to leave the antenna outdoors
length of time.
Alternate methods of
An alternative frame assembly may be made out
or 1" aluminum angle iron. It is important that the front
and rear rows are
from each other regardless of your construction
Use plastic or a dense hardwood for the spreaders.
If you use metal, be sure you leave a fairly thick
insulator of plastic to minimize DC and capacitive
between the sections.
Non-corroding hardware such as brass, nylon
stainless is highly recommended on any
antenna rotated 90 degrees for horizontal
polarization - you may wish
to lengthen the design a
bit for the "low" end of the SSB portion of
Formulas, and examples:
(Includes 2 meter
and 440 examples)
Front elements 248/147 = 1.68 feet X 12 = 20.24"
[6.72” @ 443]
[20.64" @ 144]
263/147 =1.78 feet X 12 = 21.46" @
[7.13” @ 443]
11808/147 = 1 wavelength front and rear = 80.32" @
[26.65” @ 443]
[82.01" @ 144]
.15 wavelength spacing =
80.32 X .15 =12.04" @ 147
[3.99” @ 443]
[12.31" @ 144]
formulas are not exact but should be close,
as stated earlier.)
Many thanks to N0UHJ for his valuable assistance with the
testing and his input to this project. Thanks Joseph!
Refer to the
"Bobtail Beam Project"
for more info.
Monitor police, fire, ham
radio, rescue, ships and
Hamuniverse.com uses Green Geeks Web